Abstract Glioblastoma (GBM) is the most common primary malignant brain tumor with poor prognosis. Therapeutic suppression of immune checkpoint molecules elicits a tumor immune response and improves long-term survival in several types of cancers. GBM cells highly express immune checkpoint molecules including programmed death-ligand 1 (PD-L1) a critical ?don?t find me? signal to the adaptive immune system, and CD47, a ?don?t eat me? signal to the innate immune system as well as a regulator of the adaptive immune response. Although radiation therapy has been shown to counteracts the immunosuppressive GBM microenvironment by enhancing the presentation of normally suppressed tumor-associated antigens, promoting CD8+ T cell recruitment, radiation enhances even further the expression of PD-L1 on tumor and microenvironment. Unfortunately, little effect has been observed with checkpoint inhibitors against GBM. An effective GBM therapy requires a delivery system that reaches the tumor in the brain, with limited systemic effect. Endogenous small vesicles known as extracellular vesicles (EVs) hold a great promise as a delivery vehicle given their unique properties including low immunogenicity and innate stability. However, intravenous delivery of EVs to the brain remains a major challenge due to poor targeting of unmodified EVs, which can be improved by surface modification. Our preliminary results shows that The cyclo(Arg-Gly-Asp- D-Tyr-Lys) peptide, which exhibits high affinity to integrin ?v?3 on tumor vascular endothelial cells, could be conjugated on EVs surface (derived from FDA-approved normal neural progenitor cells), resulting in improved EV accumulation in brain tumors after intravenous administration. Furthermore, building on recent studies showing that short bursts of radiation therapy can prime tumors for enhanced accumulation and intratumoral distribution of nanotherapeutics in tumor-associated macrophages-dependent fashion, we showed that glioblastomas primed with radiation had an enhanced uptake of targeted EVs. In this proposal, we will take advantage of these unique characteristics of targeted EVs and load them with small interfering RNAs (siRNAs) against PD-L1 and CD47 to achieve enhanced immune response at the glioblastoma site, primed with radiation. We will evaluate whether radiation therapy will prime glioblastomas for enhanced uptake of these targeted EV across the BBB to deliver siRNAs to GBM, to increase CD8 T cells cytotoxic activity, thus halting tumor growth and prolonging animal survival in a syngeneic graft GBM mouse model.